PURPOSE: To provide an expansion/contraction guide structure which requires less components and reduces looseness of balls, and which is capable of smooth expansion/contraction guiding.

CONSTITUTION: In an expansion guide structure which guides an outer cylindrical body 1 and an inner cylindrical body 2 inserted into the outer cylindrical body 1 through plural balls 4 rotatably held in a retainer 3, an outer V groove 6 and an inner V groove 7 facing each other are longitudinally formed respectively on the inside peripheral surface of the outer cylindrical body 1 and the outside peripheral surface of the inner cylindrical body 2. Balls 4 are adapted to be rollably held between the outer V groove 6 and the inner V groove 7.